Support Measures

O&M and asset management strategies for substations and switchgear

With the electrical grid growing in complexity, finding the right op­e­rations and maintenance (O&M) strategy for substation assets is becoming increasingly important. O&M of substations and switchgear assures reliable supply and failure reduction. Asset management and maintenance is carried out when certain indicators give the signal that the equipment is deteriorating, and the probability of failure is increasing. Various strategies, whether time, condition or reliability based, can enable a dra­stic reduction of the costs associated with maintenance, thereby curtailing the incidence of serious faults, and optimising resources. An unpredicted breakdo­wn in a substation or switch­gear can lead to massive time and cost overruns for utilities. Substa­tion asset maintenance also involves periodic pla­n­ned inspections, checking, testing and trouble­shooting to ensure the correct operation and interaction of all components over a plant’s life cycle.

O&M strategies

Various key maintenance strategies have been established over the years for the maintenance of the principal assets of substations.

Under time-based maintenance, typically, periodic maintenance is carried out according to the manufacturer’s ge­neric maintenance schedule. This may also include the provision of spare parts and consumables, and the replacement of worn-out portions or systems during the substation’s service life.

For condition-based maintenance (CBM), maintenance is planned according to the condition of the equipment. CBM of substation assets can be undertaken through a combination of intelligent electronic devices, smart sensors, etc. Moreover, the actual condition of the equipment is constantly assessed th­rough online detection of significant wo­rking device strictures, and their automatic comparison with average values and functioning parameters.

Relia­bility-based  maintenance is another method that can be considered. Sub­sta­tion reliability modelling enables customers to comprehend the risk link­ed to each of its components. Reliability-centred maintenance is based on optimising maintenance investment by limiting the execution of redundant tasks while concentrating on the substation components that are representative of higher risk. This evaluation includes “fail­­ure mode and effect analysis” for determination of the best maintenance strategy to retain reliability. Further­more, the life cycle cost-based evaluation of this approach has to be derived from CBM analysis.

For switchgear power systems, maintenance strategies are broadly similar and can be preventive, corrective, or, less co­m­monly, predictive. Preventive maintenance is key to keeping a system working properly, and entails regular, annual inspection of components. Fur­ther, the components should be tested to ensure smooth functioning, since even slight uninterrupted vibrations can damage the equipment. Predictive maintenance methods are useful for condition-based monitoring of swit­chgear equipment and are also used for determining when switchgear maintenance is required. Ma­intenance proce­sses are commenced based on different parameters, different methods for ac­q­uiring the condition data and, most importantly, an understanding of the degradation mechanisms that have an impact on switchgear. The­refore, intrusive and non-intrusive diagnostic tests can be conducted on switch­gear. Tests should be undertaken at the time of co­mmissioning to establish a ba­seline for future judgement.

The health of gas-insulated substation (GIS) equipment can be supervised in several ways depending on various purposes and needs. Gas monitoring is predominantly used to make sure that adequate sulphur hexafluoride (SF6) gas is provided for meeting the equipment’s requirements, typically concerning so­me arrangement of gas density monitoring. Apart from being a very good insulator, SF6 is a potential greenhouse gas, and therefore its leakage into the environment also needs to be strictly monitored. Partial discharge in the SF6-filled switchgear chambers can reduce the life and quality of insulation.

The most frequent monitoring arrangement is typically gas monitoring, but gas density measurements also have certain limitations. An online SF6 system typically comprises a gas density sensor, a data capture and processing platform, and graphical user interface software. Partial discharge monitoring has also received interest, as it promises the possibility of sending out warnings related to insulation problems in GIS installations. A GIS needs to be partial disch­arge-free. Any detection of such disch­arge above a minimum threshold is co­nstrued as an emergent difficulty. With the help of online partial discharge mo­nitor servers, data is collected from the sensor nodes and analysed. Installed software automatically translates the partial discharge movement into graphs and management reports, showing its severity, location and type. Online partial discharge monitoring allows constant monitoring of the power transformer or GIS while it is operating. This allows maintenance and operations to receive partial discharge data in real time. In comparison, offline partial discharge monitoring can be carried out when the GIS is taken offline during a scheduled outage or a normal maintenance cycle. Several technologies can be used to monitor partial discharge today. Acoustic, dissolved gas analysis and ultra high frequency technologies are the most common. Accurate interpretation of partial discharge data is essential to maintenance planning.

Conclusion

Optimising the life of ageing switchgear is not a new concern, but it continues to be a major issue for the power industry. Substations and switchgear are key elements in power systems and play a crucial role in overall business perfor­ma­nce. Well-planned substation and swit­chgear maintenance ensures reliable supply and reduction in failures. A ma­jor failure can result in significant time and cost overruns. This makes it im­perative to take optimised maintenance and replacement decisions by mo­ving from reactive to proactive ma­in­tenance, thereby reducing unpla­n­­­n­ed downtime and minimising the costs of ex­ten­ding asset life.

When it comes to asset management, some of the governing constituents of op­erating costs are maintenance and associated costs. In addition, other decisive pa­rameters must be recognised along with their impact on the overall cost. Ge­t­ting into an annual inspection routine can potentially forestall expenditure on new equipment installation or repairs, while simple maintenance processes can prolong equipment life by decreasing the likelihood of malfunctioning. Switchgear apparatus characteristically requires a low level of maintenance.

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